Method for producing toner

ABSTRACT

A toner can be produced by dispersing a colorant in a dispersion medium essentially composed of a polymerizable monomer by using a media-type dispersing device at a tip speed of a stirring body of 3 to 20 m/s with a residence time being 0.03 to 0.5 hour to obtain a monomer composition A; dispersing or dissolving a charge control agent in a dispersion medium to obtain a monomer composition B; dispersing or dissolving a parting agent in a dispersion medium to obtain a monomer composition C; mixing or dispersing the monomer composition A, the monomer composition B and the monomer composition C in a dispersion medium to obtain a polymerizable composition D; and homogenizing the composition D in an aqueous dispersion medium containing a dispersion stabilizer to generate droplets; polymerizing the droplets to obtain colored polymer particles; and attaching an outer-additive on the colored polymer particles.

BACKGROUND OF THE INVENTION

The present invention relates to methods for producing toners for use indeveloping electrostatic images to be formed by an electrophotography,electrostatic recording process and other processes, and, moreparticularly, to a method which is capable of efficiently producing atoner having a narrow particle diameter distribution and causing a lowdegree of printing fog.

A toner to be used in an electrophotography apparatus, an electrostaticrecording apparatus or another apparatus has been produced by varioustypes of methods. To take an example, a classifying method (namely,crushing method) in which, after a colorant, a charge control agent, anoffset preventing agent and other agents are uniformly dispersed in athermoplastic resin by melt-kneading processing, the resultant resin wascrushed to produce particles having a desired particle diameter. Anotherknown example is the method (namely, polymerization method) in whichdroplets of a monomer composition containing a colorant and otheradditives are polymerized and optionally aggregated to directly producetoner particles.

In such the polymerization methods, characteristics of toner particlesto be obtained depend on the uniformity of fine droplets of the monomercomposition containing a colorant and other agents.

As a method for producing the monomer composition, a method ofdispersing such that a viscosity change of more than 10 times an initialviscosity can be attained by using a media-type dispersing device hasbeen proposed (Japanese Patent Laid-Open No. 75429/1994). However, evenif a dispersion which has been subjected to such a large viscositychange is polymerized, the obtained toners have a wide particle diameterdistribution, whereupon in a long period of operation, a fog on alight-sensitive material or paper can occur to deteriorate imagecharacteristics.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of efficientlyproducing a toner which has a narrow particle diameter distribution andgenerates minimal fog.

As a result of an extensive study by the present inventors forovercoming various problems in a method for producing a toner by apolymerization method, the present inventors have found that a tonerwhich has a narrow particle diameter distribution and does not cause afog can be produced by conducting a step of dispersing a colorant andother additives in a polymerizable monomer by using a media-typedispersing device with a specified rotation speed in a specified periodof residence time and, being based on the above finding, have achievedthe present invention.

Thus, according to the present invention, there is provided a method forproducing a toner comprising the steps of: dispersing a colorant in adispersion medium, essentially composed of a polymerizable monomer, byusing a media-type dispersing device at a rate of the tip of a stirringbody of 3 to 20 m/s with a residence time being 0.03 to 0.5 hour toobtain a monomer composition A; homogenizing the above-describedcomposition A in an aqueous dispersion medium containing a dispersionstabilizer to generate droplets; and polymerizing the above-describeddroplets to obtain colored polymer particles.

Further, according to the present invention, there is provided a methodfor producing a toner comprising the steps of: dispersing a colorant ina dispersion medium (a), essentially composed of a polymerizablemonomer, to obtain a monomer composition A; dispersing or dissolving acharge control agent in a dispersion medium (b), essentially composed ofa polymerizable monomer, to obtain a monomer composition B; dispersingor dissolving a lubricant in a dispersion medium (c), essentiallycomposed of a polymerizable monomer, to obtain a monomer composition C;dispersing or mixing the monomer composition A, the monomer compositionB and the monomer composition C in a dispersion medium (d), essentiallycomposed of a polymerizable monomer, to obtain a polymerizablecomposition D; homogenizing to form droplets of the above-describedpolymerizable composition D in an aqueous dispersion medium containing adispersion stabilizer; and polymerizing the above-described droplets toobtain colored polymer particles.

DETAILED DESCRIPTION OF THE INVENTION

A production method for toner according to the present inventioncomprises the steps of: dispersing a colorant in a dispersion medium,essentially composed of a polymerizable monomer, using a media-typedispersing device at a tip speed of a stirring body of 3 to 20 m/s witha residence time being 0.03 to 0.5 hour to obtain a monomer compositionA; homogenizing the above-described composition A in an aqueousdispersion medium containing a dispersion stabilizer to generatedroplets; and polymerizing the above-described droplets to obtaincolored polymer particles.

The media-type dispersing device for use in the dispersing steps of theproduction method according to the present invention comprises a statorand a stirring body wherein the stator is provided with an opening forintroducing materials and an opening for discharging medium, colorantand so on; the stirring body is disposed in the stator in a rotatablemanner; media is filled in a space formed by the stator and the stirringbody such that the media can move with rotation of the stirring body.

As the media-type dispersing device, there are various types such as ahorizontal cylinder type, a vertical cylinder type, and an invertedtriangle type, depending on a shape or disposing manner of the stator.Specific examples are a horizontal, cylindrical media-type dispersingdevice; vertical, cylindrical media-type dispersing device; and aninverted-triangle, annular media-type dispersing device.

Specific examples of the above-described media-type dispersing devicesinclude Attritor (available from Mitsui Mining Co.), Mighty Mill(available from Inoue Seisakusho Co.), Diamond Fine Mill (available fromMitsubishi Heavy Inds.), Dyno-Mill (available from Shinmaru EnterprisesCorp.), Apex Mill (available from Kotobuki Engineering & Mfg. Co.) andother mills. Among these, a horizontal, cylindrical media-typedispersing device such as Dyno-Mill is preferable for the productionmethod according to the present invention since it is of a horizontaltype and can perform a favorable dispersion while suppressing aviscosity change.

As media filled in a media-type dispersing device, beads which areexcellent in abrasion resistance are used. The diameter of a single beadis ordinarily 0.1 to 20 mm, preferably 0.3 to 10 mm, and more preferably0.5 to 3 mm. The density of the bead is ordinarily 3 to 9 g/cm³,preferably 4.5 to 7.5g/cm³. Materials used for beads, and ceramicshaving high hardness such as zircon, zirconia and other ceramic productsand metals having high hardness such as steel and other iron productsare preferably used. Taking grinding efficiency into consideration, theapparent filling volume of the media in the dispersing device isordinarily 50 to 90% by volume, preferably 60 to 85% by volume.

In the present invention, it is necessary to set a tip speed of astirring body at 3 to 20 m/s, preferably 8 to 20 m/s. Also in thepresent invention, a residence time of the monomer composition A to bedispersed by the media-type dispersing device is 0.03 to 0.5 hour,preferably 0.05 to 0.3 hour. By setting such tip speed (rotation rate)and residence time, a toner which is excellent in an electric chargeamount distribution and does not cause a printing fog can be obtained.

In a preferred production method according to the present invention, asupply amount of the monomer composition A passing through themedia-type dispersing device is set to be at an apparent linear velocityof ordinarily 0.005 to 2 m/min, preferably 0.01 to 1 m/min. In order toset the apparent velocity to be within these ranges, the monomercomposition A to be discharged from the media-type dispersing device maybe circulated by leading it into an inlet of the dispersing device. Avolume of the monomer composition A to be held in the dispersing deviceis ordinarily 10 to 50% by volume, preferably 15 to 40% by volume.

The apparent linear velocity is calculated by the following expression:

(Apparent linear velocity[m/min])=(fluid flow[m³/min])/(cross sectionalarea of the stator[m²])

A temperature of the monomer composition A in the dispersing device isordinarily 0 to 50° C., preferably 20 to 45° C. By setting thetemperature to be within the range, a toner which is excellent in acharge amount distribution and does not cause a printing fog can beobtained.

In the production method according to the present invention, a viscosityof the monomer composition A after being dispersed is less than 10times, preferably 1 time to 8 times as much as that of the monomercomposition A before being dispersed, namely, an initial viscositythereof. By suppressing a viscosity change, a toner excellent in theelectric charge amount distribution can easily be obtained.

The dispersion medium according to the present invention is essentiallycomposed of a polymerizable monomer.

As a main component of the polymerizable monomer, a monovinyl monomercan be used. The polymerizable monomer is subjected to polymerization tobe a binding resin component in a colored polymer particle.

Specific examples of monovinyl monomers include styrene monomers such asstyrene, 4-methylstyrene, and α-methylstyrene; unsaturated carboxylicacid monomers such as acrylic acid, and methacrylic acid; unsaturatedcarboxylic acid ester monomers such as methyl acrylate, ethyl acrylate,propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate,dimethylaminoethyl acrylate, methyl methacrylate, ethyl methacrylate,propyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, anddimethylaminoethyl methacrylate; unsaturated carboxylic acid derivativessuch as acrylonitrile, methacrylnitrile, acrylamide, and methacrylamide;ethylenically unsaturated monoolefins such as ethylene, propylene, andbutylene; halogenated vinyl monomers such as vinyl chloride, vinylidenechloride, and vinyl fluoride; vinyl esters such as vinyl acetate, andvinyl propionate; vinyl ethers such as vinyl methyl ether, and vinylethyl ether; vinyl ketone monomers such as vinyl methyl ketone, andmethyl isopropyl ketone; nitrogen-containing vinyl monomers such as2-vinylpyridine, 4-vinylpyridine, and N-vinylpyrrolidone. Thesemonovinyl monomers may be used either individually or in any combinationthereof. Among these monovinyl monomers, styrene monomers, unsaturatedcarboxylic acid monomers, unsaturated carboxylic acid esters, andunsaturated carboxylic acid derivatives are preferably used.Particularly, styrene monomers and ethylenically unsaturated carboxylicacid ester monomers are favorably used.

By using an optional crosslinkable monomer as a polymerizable monomertogether with any one of these monovinyl monomers, fixing ability and,particularly, offset resistance are enhanced.

As crosslinkable monomers, there are for example, aromatic divinylcompounds such as divinylbenzene, divinylnaphthalene and derivativesthereof; polyfunctional ethylenically unsaturated carboxylic acid esterssuch as ethylene glycol dimethacrylate, and diethylene glycoldimethacrylate; N,N-divinylaniline and divinyl ether; and compoundshaving at least three vinyl groups. These crosslinkable monomers may beused either individually or in any combination thereof. It is desirablethat these crosslinkable monomers are used in a proportion of ordinarily0.05 to 5 parts by weight, preferably 0.1 to 2 parts by weight, based on100 parts by weight of the monovinyl monomers.

Further, in the present invention, a macromonomer may be used as apolymerizable monomer. The macromonomer has a polymerizable vinylfunctional group at the molecular chain terminal thereof and is anoligomer or polymer having a number average molecular weight ofordinarily 1,000 to 30,000.

As the polymerizable vinyl functional group which the macromonomer hasat the molecular chain terminal thereof, mentioned are an acryloyl groupand a methacryloyl group, with the methacryloyl group being preferredfor ease of copolymerization.

An amount of the macromonomer used is ordinarily 0.01 to 10 parts byweight, preferably 0.03 to 5 parts by weight, more preferably 0.05 to 1part by weight, based on 100 parts by weight of the monovinyl monomer.As long as the amount of the macromonomer is within these ranges, a morefavorable balance between shelf stability and fixing ability can beobtained.

A colorant is dispersed in the above-described dispersion medium.Conventional dyes or pigments as colorants for toners may be used.

Examples of black colorants include pigments such as carbon black, andnigrosine-base dyes; magnetic particles such as cobalt, nickel, triirontetraoxide, manganese iron oxide, zinc iron oxide and nickel iron oxide.Where carbon black is used, it is preferable to use carbon black havinga primary particle diameter of 20 to 40 nm since an image quality can beenhanced and also an enviromentally friendly toner is obtained.

As colorants for use in color toners, there are yellow colorants,magenta colorants, and cyan colorants.

As yellow colorants, compounds such as azo pigments, and condensationpolycyclic pigments are used. Specifically mentioned as examples thereofare C. I. Pigment Yellow No.3, 12, 13, 14, 15, 17, 62, 65, 73, 83, 90,93, 97, 120, 138, 155, 180, 181, 185, and 186.

As magenta colorants, compounds such as azo pigments and condensationpolycyclic pigments are used. Specifically mentioned as examples thereofare C. I. Pigment Red No.48, 57, 58, 60, 63, 64, 68, 81, 83, 87, 88, 89,90, 112, 114, 122, 123, 144, 146, 149, 163, 170, 184, 185, 187, 202,206, 207, 209, 251, and C. I. Pigment Violet No.19.

As cyan colorants, compounds such as copper phthalocyanine compounds andthe derivatives thereof, anthraquinone compounds are used. Specificallymentioned as examples thereof are C. I. Pigment Blue No.2, 3, 6, 15,15:1, 15:2, 15:3, 15:4, 16, 17, and 60.

These colorants are used in a proportion of ordinarily 0.1 to 50 partsby weight, preferably 1 to 20 parts by weight, based on 100 parts byweight of entire polymerizable monomers (whole quantity of polymerizablemonomers to be used for obtaining colored polymer particles). An amountof dispersion medium in the monomer composition A is 40 to 99% byweight, and preferably 70 to 95% by weight.

Further, for a purpose of uniform dispersion of the colorant in tonerparticles, a lubricant such as oleic acid and stearic acid; a dispersionassistant such as a silane coupling agent and a titanium coupling agent;a polar group-containing polymer dispersion assistant; and other agentsmay be present in the monomer composition A. Such a lubricant ordispersion assistant or both are ordinarily used in a proportion ofapproximately 1/1000 to 1/2, based on the weight of the colorant.

An average dispersed particle diameter of the colorant or other agentsin the dispersion medium after dispersion processing according to thepresent invention is preferably 1 μm or less, more preferably 0.5, μm orless.

In the production method according to the present invention, in order tocontrol characteristics of toner particles to be obtained, other agentssuch as a charge control agent, a molecular weight control agent, aparting agent and other compounding agents can be used. These agents canbe dispersed or dissolved in the dispersion medium similar to thatdescribed above separately from the colorant or in the above-describedmonomer composition A. In the production method according to the presentinvention, it is particularly preferable that the charge control agentis dispersed in the dispersion medium similar to that described aboveby, optionally, using the media-type dispersing device thereby preparingthe monomer composition B, the parting agent is dissolved in thedispersion medium similar to that described above or dispersed by,optionally using a media-type dispersing device thereby preparing amonomer composition C, and then the monomer composition A, the monomercomposition B and the monomer composition C are mixed or dispersed inthe dispersing medium similar to that described above by, optionally,using the media-type dispersing device to obtain a polymerizablecomposition D.

As the charge control agent to be used in the present invention, varioustypes of positively chargeable charge control agents or negativelychargeable charge control agents can be used. For example, metalcomplexes of organic compounds having a carboxyl group ornitrogen-containing group, metal-containing dyes, and nigrosine can beused. More specifically, charge control agent such as Spiron Black TRHand T-77 (both available from Hodogaya Chemical Co., Ltd.), BontronS-34, Bontron E-84 and Bontron N-01 (all available from Orient ChemicalIndustries Ltd.), and Copy Blue-PR (available from Clariant Ltd.);and/or charge control resins such as quaternary ammonium (or ammoniumsalt) group-containing copolymers, sulfonic acid (orsulfonate)-containing copolymers can be employed. Among the chargecontrol agents, charge control resins are preferable.

An amount of any one or any combination of the above-described chargecontrol agents to be preferably used is ordinarily 0.01 to 10 parts byweight, particularly 0.03 to 8 parts by weight, based on 100 parts byweight of entire polymerizable monomers. An amount of the dispersionmedium in the monomer composition B is 70 to 99% by weight, preferably75 to 95% by weight.

As the parting agent, used are, for example, low molecular weightpolyolefin waxes such as low molecular weight polyethylene, lowmolecular weight polypropylene, and low molecular weight polybutylene;terminal-modified polyolefin waxes such as low-molecular weightpolypropylene oxidized at its molecular chain terminal, low-molecularweight polypropylene epoxy-modified at its molecular chain terminal,block polymers of these low-molecular weight polypropylenes withlow-molecular weight polyethylene, low-molecular weight polyethyleneoxidized at its molecular chain terminal, low-molecular weightpolyethylene epoxy-modified at its molecular chain terminal, and blockpolymers of these low-molecular weight polyethylenes modified at theirrespective molecular chain terminals with low-molecular weightpolypropylene; natural plant waxes such as candelilla, carnauba, rice,Japan wax and jojoba; petroleum waxes such as paraffin, microcrystallineand petrolatum, and modified waxes thereof; mineral waxes such asmontan, ceresin and ozokerite; and synthetic waxes such asFischer-Tropsch wax; polyfunctional ester compounds such aspentaerythritol esters including pentaerythritol tetramyristate,pentaerythritol tetrapalmitate, and pentaerythritol tetralaurate, anddipentaerythritol esters including dipentaerythritol hexamyristate,dipentaerythritol hexapalmitate, and dipentaerythritol hexalaurate.

Among these, synthetic waxes, terminal-modified polyolefin waxes,petroleum waxes and the modified waxes thereof, and polyfunctional estercompounds are preferable. Among the polyfunctional ester compounds,pentaerythritol esters which show endothermic peak temperature uponheating within a range of 30° C. to 200° C., preferably 50° C. to 180°C. and more preferably 60° C. to 160° C. on a DSC curve determined bymeans of a differential scanning calorimeter (DSC), anddipentaerythritol esters which show endothermic peak temperature withina range of 50° C. to 80° C. are particularly preferable as a toner forthe desirable point of a balance between fixing and peeling properties.Among others, dipentaerythritol esters each of which has a molecularweight of 1000 or more, solubility in a proportion of 5 parts by weightor more, based on 100 parts by weight of styrene at 25° C. and an acidvalue of 10 mg/KOH or less exhibit a distinguished effect in lowering afixing temperature. The above-described endothermic peak temperaturesare values measured in accordance with ASTM D3418-82.

The above-described parting agents are preferably used in a proportionof ordinarily 0.1 to 20 parts by weight, particularly 1 to 15 parts byweight, based on 100 parts by weight of the entire amount ofpolymerizable monomers. An amount of dispersion medium in the monomercompound C is 70 to 99% by weight, preferably 75 to 95% by weight.

As example molecular weight control agents, mentioned are mercaptanssuch as t-dodecylmercaptan, n-dodecylmercaptan, n-octylmercaptan,halogenated hydrocarbons such as carbon tetrachloride, and carbontetrabromide. These molecular weight control agents may be contained inany of the monomer compounds A to C or added in the polymerizablecomposition before a polymerization is initiated or while apolymerization reaction is progressing. The above-described molecularweight control agents are used in a proportion of ordinarily 0.01 to 10parts by weight, preferably 0.1 to 5 parts by weight, based on 100 partsby weight of entire polymerizable monomers.

In a homogenizing process according to the present invention, themonomer composition A obtained by the above-described dispersionprocess, preferably the polymerizable composition D which has beenobtained mixing or dispersing the monomer composition A, monomercomposition B and monomer composition C in the dispersion medium similarto that described above is changed into droplets in an aqueousdispersion medium containing a dispersion stabilizer.

The aqueous dispersion medium to be used in the present invention is awater-based dispersion medium added with a dispersion stabilizer.

As example dispersion stabilizers, mentioned are sulfates such as bariumsulfate, and calcium sulfate; carbonates such as barium carbonate,calcium carbonate and magnesium carbonate; phosphates such as calciumphosphate; metal oxides such as aluminum oxide, and titanium oxide; andmetal hydroxides such as aluminum hydroxide, magnesium hydroxide, andferric hydroxide; water-soluble polymers such as polyvinyl alcohol,methyl cellulose, and gelatin; anionic surface active agents; nonionicsurface active agents; and amphoteric surface active agents. Amongothers, the dispersion stabilizer containing a metallic compound,particularly colloid of a hardly water-soluble metal hydroxide ispreferable since it can narrow a particle diameter distribution of thepolymer particles and enhance an image sharpness. Particularly, where acrosslinkable monomer is not copolymerized, the dispersing stabilizercontaining colloid of a hardly water-soluble metal hydroxide isfavorable since it enhances dispersion stability of polymer particlesduring polymerization, fixing ability and shelf stability of the toner.

The dispersion stabilizer containing colloid of a hardly water-solublemetal hydroxide does not limit its production process; however, it ispreferable to use colloid of a hardly water-soluble metal hydroxideobtained by adjusting the pH of an aqueous solution of a water-solublepolyvalent metallic compound to 7 or higher, in particular, colloid of ahardly water-soluble metal hydroxide formed by reacting a water-solublepolyvalent metallic compound with an alkali metal hydroxide in anaqueous phase.

The colloid of the hardly water-soluble metal hydroxide used in thepresent invention preferably has D50 (50% cumulative value of numberparticle diameter distribution) of number particle diameter distributionbeing at most 0.5 μm and D90 (90% cumulative value of number particlediameter distribution) thereof being at most 1 μm. If the particlediameter of the colloid is too great, the stability of thepolymerization is broken, and the shelf stability of the resultingpolymerized toner is deteriorated.

The dispersion stabilizer is used in a proportion of ordinarily 0.1 to20 parts by weight, preferably 0.3 to 10 parts by weight, based on 100parts by weight of the entire amount of polymerizable monomers. If theproportion of the dispersion stabilizer used is too low, it is difficultto achieve sufficient polymerization stability whereupon the resultingpolymers tend to coagulate with each other. On the other hand, if theproportion of the dispersion stabilizer used is too high, the particlediameter of the resulting polymerized toner tends to become too small.

In the aqueous dispersion medium according to the present invention, awater-soluble organic or inorganic compound may be contained as neededbesides the dispersion stabilizer.

Particularly, when a water-soluble oxo acid salt is contained therein,it is preferable since the particle diameter distribution becomes sharp.As examples of the water-soluble oxo acid salts, borates, phosphates,sulfates, carbonates, silicates, and nitrates are mentioned. Among otherexamples, preferably mentioned are silicates, borates or phosphates, andmore preferably borates. Examples of borates include sodiumtetrahydroborate, potassium tetrahydroborate, sodium tetraborate, sodiumtetraborate decahydrate, sodium metaborate, sodium metaboratetetrahydrate, sodium peroxoborate tetrahydrate, potassium metaborate,and potassium tetraborate octahydrate. Examples of phosphates includesodium phosphinate monohydrate, sodium phosphinate pentahydrate, sodiumhydrogen phosphinate 2.5-hydrate, sodium phosphate dodecahydrate,disodium hydrogen phosphate, disodium hydrogen phosphate dodecahydrate,sodium dihydrogen phosphate monohydrate, sodium dihydrogen phosphatedihydrate, sodium hexametaphosphate, sodium hypophosphate decahydrate,sodium diphosphate decahydrate, sodium dihydrogen diphosphate, sodiumdihydrogen diphosphate hexahydrate, sodium triphosphate, sodiumcyclo-tetraphosphate, potassium phosphinate, potassium phosphonate,potassium hydrogen phosphonate, potassium phosphate, dipotassiumhydrogen phosphate, potassium dihydrogen phosphate, potassiumdiphosphate trihydrate, and potassium metaphosphate. Examples ofsilicates include sodium metasilicate, sodium metasilicate nonahydrate,water glass, and sodium orthosilicate. An amount of any of thewater-soluble oxo acid salts is ordinarily 0.1 to 1000 parts by weight,preferably 1 to 100 parts by weight, based on 100 parts by weight ofhardly water-soluble inorganic compound colloid. The water-soluble oxoacid salts are dissolved in the water-based dispersion medium.

A method of changing the monomer composition A or the polymerizablecomposition D into droplets in the water-based dispersion medium is notparticularly limited. Ordinarily, such droplets can be obtained bystrongly stirring the monomer composition by using a high-speed mixer.The droplets are formed by using, for example, a turbine-type mixerrepresented by TK type homomixer (available from Tokushu Kika KogyouCo., Ltd.), a device represented by Ebara Milder (available from EbaraCorporation) which stirs a dispersion in a space formed between a rotorand a stator thereof by flowing the dispersion from an inside of therotor to an outside of the stator while the rotor in a comb-like shapeand the stator which are arranged in a concentric relation with eachother are rotated at a high speed, a device represented by Clear MixCLM-0.8S (available from M. Technique Co., Ltd.) for performinghomogenization by shear force generated by a rotor rotating at a highspeed and a screen surrounding the rotor, collision force, pressurefluctuation, cavitation, and potential core, a device represented by TKFilmics (available from Tokushu Kika Kogyo Co., Ltd.) for performinghomogenization by forcing the solution against a side wall of ahomogenization vessel by means of a centrifugal force thereby forming aliquid film thereon and then contacting the resultant film with a tip ofa stirring body which is rotating at an extremely high speed. A particlediameter of the thus formed droplets is homogenized approximately to thesame size as that of the colored polymer particles obtained afterpolymerization. A particle diameter of the thus formed droplets isordinarily 0.5 to 15 μm, preferably 1 to 10 μm.

The polymerizable monomers in the composition A or D which have beenhomogenized in the aqueous dispersion medium are polymerized by apolymerization initiator to obtain colored polymer particles. Apolymerization reaction can be performed under an ordinary polymerpolymerization condition. In order to increase the particle diameter,the polymer particles may be stirred strongly to be aggregated aftersuch a polymerization reaction has taken place.

As polymerization initiators, mentioned are persulfates such aspotassium persulfate, and ammonium persulfate; azo compounds such as4,4′-azobis(4-cyanovaleric acid), 2,2′-azobis(2-amidinopropane)dihydrochloride,2,2′-azobis-2-methyl-N-1,1′-bis(hydroxymethyl)-2-hydroxyethylpropionamide, 2,2′-azobis(2,4-dimethylvaleronitrile),2,2′-azobisisobutyronitrile, and 1,1′-azobis(1-cyclohexanecarbonitrile);peroxides such as methyl ethyl peroxide, di-t-butyl peroxide, acetylperoxide, dicumyl peroxide, lauroyl peroxide, benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butyl peroxyneodecanoate, t-hexylperoxy-2-ethyl-hexanoate, t-butyl peroxypivalate, t-hexylperoxypivalate, di-isopropyl peroxydicarbonate, di-t-butylperoxyisophthalate, 1,1,3,3-tetrametyl butyl peroxy-2-ethylhexanoate,and t-butyl peroxyisobutyrate. Red-Ox initiators composed ofcombinations of these polymerization initiators with a reducing agentmay also be used. Of these polymerization initiators, oil-solubleinitiators which are soluble in polymerizable monomers used arepreferably selected. Optionally, a water-soluble initiator can be usedin combination with an oil-soluble initiator. The above-describedpolymerization initiators can be used in an amount of ordinarily 0.1 to20 parts by weight, preferably 0.3 to 15 parts by weight, and morepreferably 0.5 to 10 parts by weight based on 100 parts by weight ofentire polymerizable monomers. The polymerization initiators canpreviously be added to the monomer composition A or the polymerizablecomposition D; they can optionally be added thereto after ahomogenization process has been terminated.

After the colored polymer particles are obtained, a surface of theabove-described colored polymer particles may further be covered with apolymer (that is shell polymer). Examplary methods of such covering withthe shell polymer, are a method of adding a monomer for use in acovering polymerization to a reaction solution containing thethus-obtained colored polymer particles thereby performing a furtherpolymerization, and a method of obtaining the colored polymer particles,adding a given polymer component to the thus-obtained colored polymerparticles and allowing it to be adsorbed or fixed thereon. When a toneris produced by using core-shell type polymer particles in which thecolored polymer particles are softened (for example, a glass transitiontemperature thereof is lowered) compared with the shell polymer, aso-called capsule type toner which has a favorable balance betweenlow-temperature stability and high-temperature shelf stability can beobtained.

The above-described polymer particles are rinsed, dehydrated and dried.A rinsing operation is preferably performed such that an amount of ametallic ion remaining in a particle is reduced. Particularly, when ametallic ion of magnesium or calcium remains in the particle, it mayoccur that a toner absorbs moisture under a high humidity condition toreduce flowability thereof or to give an adverse effect to an image. Thetoner which has a low content of magnesium or calcium remaining in thetoner (hereinafter referred to simply as residual metal) can obtain afavorable image under the conditions of high temperature and highhumidity, which has a high printing density and is free from a fog by ahigh-speed printer having a printing capacity of at least 30 sheets aminute. An amount of the residual metal is preferably 170 ppm or less,more preferably 150 ppm or less, and most preferably 120 ppm or less. Inorder to reduce the amount of the residual metal, for example, when theparticles are subjected to rinsing and dehydration operations, they aredehydrated and rinsed by a rinsing and dehydrating device such as acontinuous belt filter or siphon-pillar-type centrifuge and thereafterdried. The resulting dried particles can optionally be classified.

The preferred toner obtained by the production method according to thepresent invention is substantially spherical. It is desirable that avolume average particle diameter (dv) thereof is 1 to 10 μm, preferably3 to 8 μm; a ratio (dv/dn) of the volume average particle diameter (dv)to a number average particle diameter (dn) thereof is 1 to 1.5,preferably 1 to 1.3; a quotient (Sc/Sr) obtained by dividing an area(Sc) of a circle with a diameter being an absolute maximum length of aparticle by a real projected area (Sr) of the particle is in a range of1 to 1.3; further, a product (Ssa×dn×G) of a specific surface area (Ssa)[m²/g] as measured in accordance with a BET method, the number averageparticle diameter (dn) [μm] and a true specific gravity (G) is in arange of 5 to 10.

A melt viscosity at 120° C. of particularly preferred toners is 100,000poise or less, preferably 0.1 to 100,000 poise, and more preferably 1 to80,000 poise. A viscosity measurement may be conducted by a flow tester.When toners having such a melt viscosity are employed, a high qualityimage can be obtained even by high-speed printing.

Further, the colored polymer particle may be treated with anouter-additive. By attaching an outer-additive on a surface of theparticle, or sticking it in the particle, a charge property,flowability, and shelf stability of the particle can be adjusted.

As outer-additives, mentioned are inorganic particles, organic acid saltparticles, and organic resin particles. Examples of the inorganicparticles include silicon dioxide, aluminum oxide, titanium oxide, zincoxide, tin oxide, barium titanate, and strontium titanate. Examples ofthe organic acid salt particles include zinc stearate, and calciumstearate. Examples of the organic resin particles include polymerparticles of methacrylate, polymer particles of acrylate, copolymerparticles of styrene-methacrylate, copolymer particles ofstyrene-acrylate, core-shell type polymer particles having a shellformed of a methacrylate copolymer and a core formed of a styrenepolymer. Among these outer-additives, the inorganic particles,particularly silicon dioxide particles, are preferable. The surface ofthese particles may be reformed by hydrophobic treatment. Thehydrophobic reformed particles, particularly the hydrophobic reformedsilicon dioxide particles, are preferable. An amount of theouter-additives is not particularly limited, but is ordinarily 0.1 to 6parts by weight, based on 100 parts by weight of the colored polymerparticles. The outer-additives can be used individually or incombination. When the outer-additives are used in combination, it ispreferable to use different types of inorganic particles different inaverage particle diameters from each other, or a combination ofinorganic particles and organic resin particles. In order to fix theouter-additive on the surface of the colored polymer particles, theouter-additive and the colored polymer particles are charged in a mixersuch as Henschel mixer for stirring.

The present invention will hereinafter be described more specifically bythe following Examples and Comparative Examples. However, the presentinvention should not be interpreted to be limited to these Examples inany way. Unless stated otherwise, all parts and percentages are given byweight.

Physical properties in the following Examples and Comparative Exampleswere measured in accordance with the following respective methods.

(1) Particle Diameter, and Ratios of Coarse Powders and Fine Powders

A volume average particle diameter (dv), a number average particlediameter (dn), a coarse powder ratio and a fine powder ratio of polymerparticles (=toner particles) were measured by means of Multisizer(available from Beckman-Coulter Inc.). The measurement by Multisizer wasconducted under the following conditions:

aperture diameter: 100 μm;

medium: Isotone II;

concentration: 10%;

number of particles subjected to measurements: 100,000.

A ratio of 16 μm or more on a cumulative curve of the volume averageparticle diameter obtained by using the above-described measuring deviceis determined as coarse powder ratio (volume %) while a ratio of 5 μm orless on a cumulative curve of the number average particle diameter isdetermined as fine powder ratio (number %).

(2) Evaluation of Image

After a non-magnetic one-component developing system printer (12 sheetdevice) was allowed to stand for one whole day(24 hours) underenvironmental conditions of 23° C. and 50% moisture, printing wascontinuously conducted from the beginning until specific sheets wereprinted and then half-tone printing was subsequently conducted until thetotal number of printed sheets reached 10,000 for evaluating printingdensity and fog. Quality of the printed images were evaluated by thefollowing index:

Printing density was evaluated and recorded by a small circle denotinggood; a delta denoting some inferior characteristics; and an x denotinggenerally inferior. Fog was evaluated and recorded by a small circledenoting good; a delta denoting some inferior characteristics; and an xdenoting generally inferior.

EXAMPLE 1

20 parts of carbon black (available from Mitsubishi Chemical Corporationunder the trade name of “#25B”) were added to 80 parts of styrene andmixed to prepare a mixture; the resulting mixture was dispersed by usingan overflow-type horizontal cylindrical media-type dispersing devicewhich was previously filled with steel beads as media having a diameterof 1.5 mm and a density of 7.4 g/cm³ at an apparent filling rate of 75volume % under conditions that a tip speed of a stirring body of themedia-type dispersing device was about 9 m/s, a residence time of themixture was 0.1 hour. an apparent linear velocity was 0.16 m/min and atemperature in the dispersing device was about 35° C. such that aviscosity of the mixture became to be about 4 times the viscosity of themixture before dispersed to obtain a monomer composition A. Theviscosity of the monomer composition A before dispersed and that of themonomer composition A after dispersed were 22 mPa·s and 86 mPa·s,respectively.

Separately, 10 parts of a charge control agent (available from HodogayaChemical Co., Ltd. under the trade name of “Spiron Black TRH”) weredispersed in 90 parts of styrene under same conditions as theabove-described conditions to obtain a monomer composition B.

Further separately, 10 parts of a parting agent (Fischer-Tropsh waxhaving an endothermic peak temperature of 100° C.; available from SasolIncorporated under the trade name of “Paraflint Spray 30”) weredispersed in 90 parts of styrene under same conditions as theabove-described conditions to obtain a monomer composition C.

35 parts of the monomer composition A (containing 7 parts of #25B), 10parts of the monomer composition B (containing 1 part of Spiron BlackTRH) and 20 parts of the monomer composition C (containing 2 parts ofParaflint Spray 30) were mixed to prepare a mixture into which 28 partsof styrene, 17 parts of n-butylacrylate, 0.3 part of polymethacrylicester macromonomer (available from Toagosei Chemical Industry Co. Ltd.under the trade name of “AA6” having a Tg of 94° C.), 0.5 part ofdivinylbenzene and 1.2 part of t-dodecylmercaptan were added and mixedin a mixing tank. An initial viscosity of the resultant mixture was 10mPa·s. Then, the resultant mixture was subjected to dispersionprocessing under same conditions as the above-described conditions toobtain a polymerizable composition D. A viscosity thereof after suchprocessing was 41 mPa·s.

On the other hand, an aqueous solution with 6.2 parts of sodiumhydroxide dissolved in 50 parts of ion-exchanged water was graduallyadded to an aqueous solution with 10.2 parts of magnesium chloridedissolved in 250 parts of ion-exchanged water under stirring to preparea colloidal solution of magnesium hydroxide. A particle diameterdistribution of colloids in the thus prepared colloidal solution wasmeasured by means of a microtrack particle diameter distributionmeasuring device (available from Nikkiso Co., Ltd.) and found to be 0.35μm in terms of D50 (50% cumulative value of number particle diameterdistribution) and 0.84 μm in terms of D90 (90% cumulative value ofnumber particle diameter distribution). Measurement by means of themicrotrack particle diameter distribution measuring device was performedunder the following conditions:

measuring range: 0.12 to 704 μm;

measuring time: 30 seconds; and

medium: ion-exchanged water.

The polymerizable composition D prepared above was added into thecolloidal solution of magnesium hydroxide obtained above and stirreduntil droplets formed came to be in a stable state; then, 6 parts oft-butyl peroxy-2-ethylhexanoate were added to the thus mixed, stirredsolution to prepare a mixture; subsequently, the thus-prepared mixturewas subjected to droplets homogenization processing by means of EbaraMilder MDN303V (available from Ebara Corporation) under conditions thata rotation rate of a rotor was 12,000 rpm, a flow rate of the mixturewas 120 liters/hour, and the mixture was forced to pass through theEbara Milder five times repeatedly to prepare an aqueous solution inwhich droplets were formed; thereafter, the thus-prepared aqueoussolution containing droplets of the polymerizable composition D wascharged into a reactor equipped with an agitating blade to initiate apolymerization reaction at 85° C.; then, after the polymerizationreaction was allowed to proceed for 4 hours holding a reactiontemperature at 90° C., the reaction was terminated to obtain an aqueousdispersion of polymer particles.

The thus-obtained aqueous dispersion of the polymer particles was rinsedwith sulfuric acid (25° C. for 10 minutes) while stirring to adjust thepH thereof to be 6 or less. The dispersion was subjected tofiltration-separation processing (filtration processing, rinsingprocessing and dehydration processing) to collect a solid content. Thethus-collected solid content was dried at 45° C. for 2 days by a dryerto obtain colored polymer particles.

To 100 parts of the thus-obtained colored polymer particles, added was0.8 part of silica having an average particle diameter of 14 nm(available from Nippon Aerosil Co., Ltd. under the trade name of“RX200”) which had been subjected to a hydrophobicity-impartingtreatment; the resultant mixture was mixed by means of a Henschel mixerto prepare a toner for electrophotography. Evaluation results thereofare shown in Table 1.

TABLE 1 Comparative Examples Examples 1 2 1 2 Residence times (hours)0.1 0.26 0.02 0.70 Tip speeds of stirring body (m/s) 9 17 22 2 Monomercomposition A Initial viscosities (mPa · s) 22 22 22 22 Viscositiesafter processed (mPa · s) 86 180 54 38 Polymerizable composition DInitial viscositics (mPa · s) 10 15 8 8 Viscosities after processed (mPa· s) 41 86 28 21 Particle diameter distributions dv (μm) 7.6 7.9 9.6 8.2dv/dn (-) 1.19 1.15 1.65 1.53 Rates of coarse powders (%) 2.2 2.8 5.04.5 Rates of fine powders (%) 14.8 15.8 35.8 23.7 Printing density ∘ ∘ ΔΔ Fog ∘ ∘ x x

EXAMPLE 2

A dispersion was obtained in the same manner as in Example 1 except thatthe tip speed value of the stirring body was changed into about 17 m/s,and the residence time was changed into 0.26 hour. The initial viscosityof the monomer composition A was 22 mPa·s while the viscosity thereofafter processed was 180 mPa·s. The initial viscosity of thepolymerizable composition D was 15 mPa·s while the viscosity thereofafter processed was 86 mPa·s. Evaluation results are shown in Table 1.

Comparative Example 1

A dispersion was obtained in the same manner as in Example 1 except thatthe tip speed value of the stirring body was changed into about 22 m/s,and the residence time was changed into 0.02 hour. The initial viscosityof the monomer composition A was 22 mPa·s while the viscosity thereofafter processed was 54 mPa·s. The initial viscosity of the polymerizablecomposition D was 8 mPa·s while the viscosity thereof after processedwas 28 mPa·s. Evaluation results are shown in Table 1.

Comparative Example 2

A dispersion was obtained in the same manner as in Example 1 except thatthe tip speed value of the stirring body was changed to about 2 m/s, andthe residence time was changed to 0.7 hour. The initial viscosity of themonomer composition A was 22 mPa·s while the viscosity thereof afterprocessed was 38 mPa·s. The initial viscosity of the polymerizablecomposition D was 8 mPa·s while the viscosity thereof after processedwas 21 mPa·s. Evaluation results are shown in Table 1.

According to the production method of the present invention, a tonerexcellent in electric charge amount distribution causing no fog canefficiently be obtained. This toner can favorably be used in ahigh-speed printer or a high-speed copier.

What is claimed is:
 1. A method for producing a toner comprising thesteps of: dispersing a colorant in a dispersion medium essentiallycomposed of a polymerizable monomer with a media-type dispersing deviceat a tip speed of a stirring body of about 3 to 20 m/s with a residencetime being about 0.03 to 0.5 hour to obtain a monomer composition A;homogenizing said composition A in an aqueous dispersion mediumcontaining a dispersion stabilizer to generate droplets; andpolymerizing said droplets to obtain colored polymer particles.
 2. Themethod for producing a toner according to claim 1, wherein the tip speedof a stirring body is about 8 to 20 m/s.
 3. The method for producing atoner according to claim 1, wherein the residence time is about 0.05 to0.3 hour.
 4. The method for producing a toner according to claim 1,wherein a diameter of media filled in the media-type dispersing deviceis about 0.1 to 20 mm.
 5. The method for producing a toner according toclaim 1, wherein a density of a bead as the media filled in themedia-type dispersing device is about 3 to 9 g/cm³.
 6. The method forproducing a toner according to claim 1, wherein the amount of residualmetal in the colored polymer particles is not more than about 170 ppm.7. The method for producing a toner according to claim 1, wherein aviscosity of the monomer composition A obtained after dispersion is lessthan 10 times that of said monomer composition A before dispersion. 8.The method for producing a toner according to claim 1, wherein atemperature of said monomer composition A to be dispersed in saidmedia-type dispersing device is about 0 to 50° C.
 9. The method forproducing a toner according to claim 1, wherein the polymerizablemonomer is styrene monomer and/or ethylenically unsaturated carboxylicacid ester monomer.
 10. A method for producing a toner comprising thesteps of: dispersing a colorant in a dispersion medium (a) essentiallycomposed of a polymerizable monomer with a media-type dispersing deviceat a tip speed of a stirring body of about 3 to 20 m/s with a residencetime being about 0.03 to 0.5 hour to obtain a monomer composition A;dispersing or dissolving a charge control agent in a dispersion medium(b) essentially composed of a polymerizable monomer to obtain a monomercomposition B; dispersing or dissolving a parting agent in a dispersionmedium (c) essentially composed of a polymerizable monomer to obtain amonomer composition C; mixing or dispersing the monomer composition A,the monomer composition B and the monomer composition C in a dispersionmedium (d) essentially composed of a polymerizable monomer to obtain apolymerizable composition D; homogenizing to form droplets of saidpolymerizable composition D in an aqueous dispersion medium containing adispersion stabilizer; and polymerizing said droplets to obtain coloredpolymer particles.
 11. The method for producing a toner according toclaim 10, wherein a residence time is about 0.05 to 0.3 hour.
 12. Themethod for producing a toner according to claim 10, wherein a diameterof media in the media-type dispersing device is about 0.1 to 20 mm. 13.The method for producing a toner according to claim 10, wherein adensity of a bead as the media in the media-type dispersing device isabout 3 to 9 g/cm³.
 14. The method for producing a toner according toclaim 10, wherein the amount of residual metal in the colored polymerparticles is not more than about 170 ppm.
 15. The method for producing atoner according to claim 10, wherein a viscosity of the monomercomposition A obtained after dispersion is less than 10 times that ofsaid monomer composition A before dispersion.
 16. The method forproducing a toner according to claim 10, wherein a temperature of saidmonomer composition A to be dispersed in said media-type dispersingdevice is about 0 to 50° C.
 17. The method for producing a toneraccording to claim 10, wherein a viscosity of the polymerizablecomposition D obtained after dispersed is less than 10 times that ofsaid polymerizable composition D before dispersed.
 18. The method forproducing a toner according to claim 10, wherein the polymerizablemonomer is styrene monomer and/or ethylenically unsaturated carboxylicacid ester monomer.
 19. The method for producing a toner according toclaim 10, wherein the colorant is selected from a group consisting ofblack colorants, magenta colorants, yellow colorants and cyan colorants.20. The method for producing a toner according to claim 10, wherein thecharge control agent is a charge control resin.